Computational Biomechanics of Human Spine Under Wrapping Compression Loading

Abstract

Abstract Computational biomechanics of the human spine under a novel compression loading that follows the curvature of the spine is performed by evaluation and comparison of the detailed response of the spine under various types of compression loading at different postures. The nonlinear finite element formulation of wrapping elements sliding without friction over solid body edges is developed and used to study the load-bearing capacity of thoracolumbar (T1-S1) and lumbosacral (L1-S1) spines under one or several wrapping compression forces. Follower load at the L1, axially-fixed compression at the L1, and combined axially-fixed compression plus constrained rotations are also considered for comparison. Moreover, for the detailed lumbosacral model, the effect of changes in the position of wrapping elements and in the lumbar curvature on results are considered. The idealized wrapping loading substantially stiffens the spine allowing it to carry very large compression loads without hypermobility. It diminishes local segmental shear forces and moments as well as tissue stresses. In comparison to fixed axial compression, therefore, the compression loading by wrapping elements that follow the spinal curvatures increases the load-bearing capacity in compression and provides a greater margin of safety against both instability and tissue injury. These findings suggest a plausible mechanism in which postural changes and muscle activation patterns could be exploited to yield a loading configuration similar to that of the wrapping loading. To alleviate hypermobility in compression, the wrapping loading could also allow for the application of meaningful compression loads in experimental as well as model studies of the multi-segmental spinal biomechanics.